Heavy hydrocarbon oils such as atmospheric distillation residual oil obtained by treating crude oil using an atmospheric distillation unit and vacuum distillation residual oil obtained by further treating atmospheric distillation residual oil using a vacuum distillation unit contain a large amount of sulfur compounds and heavy metal compounds. When these heavy hydrocarbon oils are supplied for general use, as a countermeasure for preventing air pollution caused by sulfur oxide, it is required to further reduce the amount of sulfur compounds contained in the heavy hydrocarbon oils. On the other hand, as crude oil has become heavy globally, there has been a tendency for crude oil containing large amounts of sulfur compounds and heavy metal compounds needing to be treated. In a step of obtaining low-sulfur heavy oil by subjecting such heavy hydrocarbon oils to a hydrogenation treatment, large amounts of heavy metal compounds such as nickel and vanadium present in the heavy hydrocarbon oils are deposited on a catalyst. When large amounts of heavy metal compounds are deposited on a catalyst, catalytic activity is reduced and catalyst life is significantly reduced due to large amounts of the deposited heavy metal compounds. Thus, the conditions for obtaining low-sulfur heavy oil have become more stringent.
Therefore, improvements in activity and life of a hydrogenation treatment catalyst for hydrogenation treatment of heavy hydrocarbon oil have been studied intensively. For example, in a hydrogenation treatment catalyst in which a hydrogenation-active component is supported on a porous alumina carrier, it is possible to maintain high desulfurization activity in a hydrogenation treatment for heavy hydrocarbon oil and catalytic activity for a long period of time by adjusting a catalyst pore distribution to be in a specific range (for example, refer to PTL 1).
On the other hand, heavy hydrocarbon oil is required to have improved storage stability. Hydrogenated heavy hydrocarbon oil is stored under heating to maintain fluidity until shipping in consideration of workability at the time of shipping. In addition, the oil may be stored for a long period of time after the oil is shipped as a product before use. Therefore, depending on a thermal history and the atmosphere at the time of storage, sediment is produced while the oil is stored and this sediment may cause plugging of a filter or damage a pump.
There are several reasons why sediment is produced, the stability of asphaltene contained in heavy hydrocarbon oil being one to be considered. When asphaltene is surrounded by resin, the asphaltene is dispersed in heavy hydrocarbon oil without producing sediment. However, when resin is dissociated from asphaltene by a hydrogenation treatment and the balance between the asphaltene and the resin collapses, the asphaltene easily appears as sediment.